<Window
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" mc:Ignorable="d" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" Height="320" Width="455">
    <StackPanel>
        <Button Width="200" Height="50">explict size</Button>

        <Expander Header="AlignmentDemo" BorderThickness="3" BorderBrush="Red">
            <StackPanel>
                <Button HorizontalAlignment="Left">left alignment</Button>
                <Button HorizontalAlignment="Right">right alignment</Button>
                <Button HorizontalAlignment="Center">center alignment</Button>
                <Button HorizontalAlignment="Stretch">stretch alignment (default)</Button>
            </StackPanel>
        </Expander>

        <Button Margin="20 10">with margin</Button>
        <Button Padding="10 4">padding but stretch</Button>
        <Button Padding="10 4" HorizontalAlignment="Center">padding and center</Button>

    </StackPanel>
</Window>